Optical waveguide splicer for linking optical fibers in a material fit

ABSTRACT

The invention concerns an optical fiber splicing device (LWL-SPG) for substance-determined connection of optical fibers (F 1 , F 2 ) by means of an electric corona discharge (GEG). A corona discharge guide (LBF 11/12 , LBF 2 , LBF 3 ) is arranged over the electrodes (E 1 , E 2 ) for the stabilization of the conditions during the splicing process.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a 371 of PCT/DE00/0330, filed Sep. 25, 2000.

FIELD OF THE INVENTION

The invention concerns an optical fiber splicing device forsubstance-determined connection of optical fibers with a device for theapproaching of the ends of two fibers, a positioning device for equalaxis alignment of the ends of the optical fibers as well as electrodesfor producing an electrical corona discharge for the splicing of theends of the optical fibers.

BACKGROUND OF THE INVENTION

A multitude of optical fiber splicing devices are available, by whichthe ends of optical fibers are connected to each other by “thermalsplicing”. The processes used for this are suitable for singlemode aswell as multimode optical fibers as well as for fiber ribbons. Thesubstance-determined connection of the ends of the fibers takes place byheating and fusion by means of corona discharge, which occurs betweentwo electrodes. In the formation of an optical fiber network asignificant number of connections have to be made, so that adequateoptical fiber splicing devices were developed. By means of these devicesthe processing steps necessary for connections such as the approachingof the ends of the optical fibers to be connected, their positioning andalignment and finally the actual splicing were coordinated and broughttogether into specially designed optical fiber splicing devices.Additionally, suitable lighting and monitoring instruments are used inthese devices, through which the progress of the process can bemonitored.

Such optical fiber splicing devices can be found in the followingliterature:

-   Telekom report 19 (1956), issue 1; pages 39–42-   Telekom report 18 (1995), issue 3; pages 136–139-   Telekom report 13 (1990), issue 2; pages 62–65-   Telekom report 9 (1986), issue 3; pages 197–201-   ICCS and Future-Link; catalogue 1998; Siemens-Communications-Cable    Networks; pages 107–116-   DE4235924-C2

The attenuation of a splice connection performed with such an opticalfiber splicing device depends on the exact alignment of thelight-guiding fiber cores, the quality of the fiber end faces and on therelevant splicing parameters selected. Thus in thermal connectiontechnology, optical waveguides or optical fibers, respectively,(referred to as “fiber” in the following) are spliced together byheating two exactly aligned fiber ends to melting temperature. In thisviscous state, the two ends of the fibers are pushed into each other, sothat it leads to the mutual fusion of the ends of the fibers and theyare thereby thermally connected. The fiber heating is performed by acorona discharge, which builds up after igniting between two electrodes.

The desired objective of the thermal connection technology is theformation of splice connection with the least possible attenuationvalues. With a modern splicing device under favorable conditions, medianattenuation values under 0.02 dB are possible. In order to realize theselow attenuations, precisely set parameters, so-called splice parameters,are necessary in addition to exactly prepared fiber ends. Importantsplice parameters include splicing voltage, splicing time, and thethrust with which the fiber ends are pushed towards each other. Theperfectly set splicing voltage causes an optimal viscosity of the fiberends during heating by the electrical corona discharge, so that inconcert with the set splicing time and the set thrust, spliceconnections with small attenuation result. Optimal splicing results canonly be obtained with optimal outside conditions (no air movement,normal humidity and room temperature, steady atmospheric pressure andother parameters) and with the perfect condition of the splicing device.It is also especially important that there are no contaminations of theelectrodes and the fiber guides.

During prolonged use of the optical fiber splicing device, a certaincontamination due to material diffusion during the splicing process andburning off of the electrodes occurs. Thus, a higher impedance resultsat the contamination point, so that the corona discharge avoids thispoint, that is, the corona discharge does not build up equally aroundthe electrode tip. During the next splicing process, an evaporation ofthe old contamination occurs in addition to new material diffusion,which then settles again on the electrodes. It can be seen from this,that in the course of time very variable conditions result on theelectrodes, which can uncontrollably alter the condition of the coronadischarge. The corona discharge is then no longer stable between the twoelectrodes and a flickering of the corona discharge results. A furthercause for an unstable corona discharge can also be found in the surfacecondition of the electrode tips. A rough electrode, not formedrotation-symmetrical, can also lead to a flickering corona discharge dueto thermal air movement created during the splicing process. This leadsto irregular, not reproducible fiber heating. The result of this, thatthe quality of the fiber connection in certain cases can vary greatly.With flickering of the corona discharge it can happen that the area ofthe greatest heating forms above or below the splice point, so that theoriginally expected heating at the ends of the fibers is not achieved,or is not achieved in a timely manner. Looking in the fiber longitudinaldirection, an unstable corona discharge thus leads to a heating of alarger fiber area in comparison to heating with clean electrodes. Thesedeviations cause an irregular fiber heating at the splice point evenwith unchanged splicing voltage, which results in an undefined materialflow. This leads to a deterioration of the splice attenuation result.Besides the electrode contamination, flickering corona discharge canalso be caused by air movement, where the previously mentioned problemscan also occur. Additionally, due to burning off of the electrodes,changes in the electrical corona discharge can occur, since the distancebetween the electrodes increases.

With such thermal splicing devices, the electrodes and the environmentof the corona discharge are completely open, so that the coronadischarge is completely exposed to the environmental conditions. Withthese devices, the avoidance of an unstable corona discharge can only beachieved by constantly cleaning or replacing the electrodes. Anotherpossibility for avoiding the instability would be an adjustment of thesplicing voltage, so that the fiber temperature at the splice pointcorresponds to the ideal temperature. This is, however, verytime-consuming and leads to only a conditional improvement of thesplicing results since constantly changing temperature conditions at thesplice point result due to the non-reproducible flickering of the coronadischarge. Additionally, it is not possible to remove the effects of theasymmetrical fiber heating by such means.

The present invention has the objective to stabilize the coronadischarge during thermal splicing of optical fibers in an optical fibersplicing device. This objective is achieved with an optical fibersplicing device of the initially explained type, by arranging a coronadischarge guide in the area of the corona discharge surrounding theelectrodes.

A decisive advantage over the state of the art technology lies in thefact that a corona discharge guide is added in the construction of thecorona discharge area according to the invention, with which theelectrodes and the corona discharge are largely protected againstenvironmental influences. This corona discharge guide consistsessentially of a surrounding tube or profile body, in whose inner spacethe corona discharge is constructed. Two small tubes are insertedbetween the two electrodes into the corona discharge length, so that thecorona discharge is guided within the tubes to the immediate area at theends of the optical fibers to be connected. The dimensions of the tubeshave to be such that the same temperature conditions exist at the endsof the fibers with clean, non-flickering electrodes as without tubes,that is, the corona discharge has to be able to spread unimpeded in eachcase. As mentioned before, a flickering corona discharge results intemporary direction changes of the corona discharge, which leads to thedescribed irregularities. Such a detour or deflection is avoided due tothe measures according to the invention based on the spatial guiding ofthe electrical corona discharge in the area of the electrodes. Thisleads to the light arc position at the splice point remaining constant,even with a local detour near the electrodes. Additionally, the use ofthe corona discharge guide has the advantage that there is less burningoff and that the increased electrode distance in the area of the splicepoint due to burning off in the area does not appear.

For the material of the light arc guide, a non-electricity-conducting,low thermal conducting material, which additionally has to be heat,ozone and UV resistant is necessary. Especially suitable is thereforeceramic or quartz glass material.

As corona discharge guide in the concept of the invention a continuoustube between the electrode can also be used, where correspondingopenings for the insertion of the ends of the fibers and correspondingobservation channels for monitoring the splicing process are provided inthe area of the connection point of the optical fibers. This leads to anadditional advantage, since the corona discharge is guided over a muchgreater area. Thus, a still better stabilization of the electricalcorona discharge can be achieved.

A further construction sample for a corona discharge guide according tothe invention results from the use of a continuous tube, which isdivided in longitudinal direction in such a way that two complimentarylongitudinal parts result. The tube should be divided into two equalparts in the longitudinal direction. It is advantageous for the lowerpart of the tube to be fastened tightly into the splicing device or thespark gap of the splicing device, respectively, and for the upper partto be attached in a hinged manner. It is advantageous to combine theupper part with the electrode hinge of the spark length so that only onehinge process is necessary. Corresponding openings for the insertion ofthe ends of the fibers and for monitoring also have to be provided herein the area of the connection point. The advantage of this constructionlies in the fact that the corona discharge is also guided and protectedover a larger area and that the ends of the fibers to be connected canbe inserted much easier at the connection point. Additionally, themechanical cleaning of the electrodes is much easier with the hingedtube.

An additional improvement of the corona discharge stability can beachieved when the necessary openings in the area of the connection pointare closed off with an additional removable cover, where only the tinyobservation channels and the insertion openings are open to theenvironment. It is also advisable that the cover is connected to theelectrode hinge so that only one hinge process has to be performed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in detail by means of eight figures.

FIG. 1 shows the splicing of optical fibers under ideal conditions.

FIG. 2 shows the conditions of the flickering electrical coronadischarge during the splicing of optical fibers.

FIG. 3 shows the corona discharge guide according to the inventionduring the slicing of optical fibers in cross-section.

FIG. 4 shows the construction according to the invention according toFIG. 3 in perspective.

FIG. 5 shows a cylindrical corona discharge guide with an opening in theconnection area.

FIG. 6 shows a corona discharge guide in a rectangular hollow profile orin layered construction.

FIG. 7 shows a spark length of an optical fiber splicing device withbuilt-in corona discharge guide.

FIG. 8 shows a diagram about attenuation measurements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 gives the condition during the splicing process during theconnection of two ends of optical fibers F1 and F2. The connection pointunder these conditions is located exactly in the center of the coronadischarge GE, which forms between the two electrodes E1 and E2. Underthese conditions, an equal heat distribution at the ends of the opticalfibers F1 and F2 exists, so that the conditions for an uneventfulconnection are given.

FIG. 2 shows two cases of unequal heat distribution during a flickeringcorona discharge GE. In the upper part of this diagram, the coronadischarge GE between the electrodes E1 and E2 is steered toward thebottom, so that the ends of the fibers F1/2 are heated only in the lowerpart by the corona discharge GE, while the upper part of the ends arenot included and thus show lower temperatures. Due to these temperaturevariations during the splicing process in this area, variable conditionsoccur, which leads, among other things, to an increase in attenuation inthe connection area of the fiber. Since this flickering of the coronadischarge GE is not regular, no reproducible results and corrections arepossible. This results in a large variation regarding the quality of theconnection points. As explained previously, the flickering of the coronadischarge GE can occur for example due to air movements or due tocontamination or due to burning off of the electrodes, where thecontamination degree due to temperature stress and wear and tear canconstantly change.

FIG. 3 illustrates the use according to the invention for a coronadischarge GEG, which in this case is formed by two separate tubes LBF11and LBF12. These tubes LBF11 and LBF12 have an inner diameter whichcorresponds to the outer diameter (approximately 1 to 2.5 mm) of theelectrodes E1 and E2, so that the tubes can be pushed onto theelectrodes E1 and E2 and be fixed there. The tubes LBF11 and LBF12 eachare positioned with an overlap of approximately 0.5 mm on the electrodesE1 and E2, respectively. The electrode distance AE is preferably 2.5 mmand the distance AR between the tubes LBF11 and LBF12 is preferably 1 to2 mm, and more preferably 1.5 mm. The wall thickness of the tubes LBF11and LBF12, respectively, is 1 to 2.5 mm. The electrodes E1 and E2 can beprovided with conical tips, where the cone angle KW preferably is 30°.Due to the stabilizing effect of the corona discharge guide, such tipsare not necessary, which would not be possible without the coronadischarge guides. In this way, less expensive electrodes can be used.The electrical corona discharge occurs between the two electrodes E1 andE2 where a part of the electrical corona discharge GEG is guided betweenthe two corona discharge guides LBF11 and LBF12 in a protected manner.

FIG. 4 illustrates the arrangement of the electrodes E1 and E2 with theadded corona discharge guides LBF11 and LBF12, as well as the ends ofthe optical fibers F1 and F2 during the splicing process in a view inperspective. It is displayed here, that the corona discharge GEG is nowguided or protected, respectively, on the basis of the corona dischargeLBF11 and LBF12, that is the form of the corona discharge GEG in itsideal form is equal or approximate, respectively, to the ideal form, sothat constant and optimal conditions for splicing of the two ends of theoptical fibers F1 and F2 exist in the connection point.

In FIG. 5 a second construction sample for a corona discharge guide LBF2according to the invention is shown. Here the guide LBF2 is a continuouscylindrical tube, which is provided with an axial longitudinal bore B.In the center area an opening A2 transverse to the longitudinal axis isapplied, which stretches below the bore B. This opening is 1 to 2 mm,preferably 1.5 mm wide and in it the two ends of the optical fibers tobe connected are inserted transverse to the longitudinal axis. The twoelectrodes of the spark length are inserted from both sides into thebore B and fixed with a distance corresponding to the givencircumstances. The corona discharge forming between the two electrodesis thus guided through the light arc guide LBF2 in a protected manner,so that nearly ideal corona discharge conditions for the splicing arepresent in the opening. Since this corona discharge guide LBF2 is formedas a continuous tube, suitable monitoring or lighting channels BK,respectively, have to be inserted in the connection area, that is in theopening A2, so that the alignment of the fibers and the subsequentsplicing process can be monitored over appropriate optical elements.Dashed lines indicate the relevant path of beams SB1 and SB2.Additionally, a cover AB1 is shown in this diagram, which can be, ifneeded, be put over the opening A2, in order to achieve furtherprotection of the connection point during the splicing process. Thiscover has to have cut-outs ALB for the corona discharge and cutouts AFfor the transverse inserted fibers, as well as monitoring and lightingchannels BK. Here the path of beams SB1 and SB2 are also indicated.

FIG. 6 shows a construction sample according to the invention for acontinuous corona discharge guide LBF3, which is based on a hollowprofile with a rectangular hollow space RH. Here again there is anopening A3 at the connection point, so that the sideways insertion ofthe ends of the optical fibers can proceed. The electrodes are locatedin the rectangular hollow space RH. Lighting and monitoring channels BK3are also provided here and the path of beams SB1 and SB2 are indicated.The opening A3 can also, if needed, be covered with a cover AB3 forbetter guidance of the corona discharge, where appropriate cutouts ALBand AF, as well as lighting and monitoring channels BK have to bepresent.

The electrodes can also be embedded or infused, respectively, into thematerial of the corona discharge guide.

FIG. 7 displays as a segment of a known optical fiber spicing deviceLWL-SPG a spark length FS, where a corona discharge guide LBF2 accordingto the invention is inserted in the area of the connection point. Inthis case, it is the corona discharge guide LBF2, which was described indetail in FIG. 5. However, the further connection in this area of theoptical fiber splicing device LWL-SPG is noticeable, especially thefrequently mentioned, but already known lighting and monitoring beampaths SB1 and SB2. Over appropriate senders, prisms P and appropriateoptical receivers OFB1 and OFB2, and in cooperation with the lightingand monitoring channels of the corona discharge guide LBF2, a correctlighting and monitoring in the area of the connection is possible. Thetwo ends of the fibers F1 and F2 to be connected are inserted verticallyto the axis of the two electrodes E1 and E2 into the opening A2 andpushed together with appropriate thrust in the formed corona dischargefor mutual fusing. Due to the protection and guidance of the coronadischarge, connections of fibers are possible under nearly equalconditions, so that steady and reducible quality can be maintained.

FIG. 8 displays a diagram showing measurement results of attenuationduring connection of fibers. From this it can be seen that splices,which are produced without a corona discharge guide (open bar display),show significantly higher attenuation values and that the dispersionarea is very large. With splices, which are produced with a coronadischarge guide according to the invention (closed bar display),significantly smaller attenuation paths resulted, which also are veryclose to each other. This can be unmistakably attributed to the fact,that the conditions at the electrodes and in the corona discharge areaare improved by the corona discharge guide according to the invention.

1. Optical fiber splicing device for substance-determined connection of optical fibers with a device for the approaching of the ends of two fibers, a positioning device for equal axis alignment of the ends of the optical fibers as well as electrodes for producing an electrical corona discharge for the splicing of the ends of the optical fibers, where a corona discharge guide (LBF11/12, LBF2, LBF3) surrounding the electrodes (E1, E2) is arranged in the area of the corona discharge (GE, GEG), the corona discharge guide (LBF11/12) being formed by two separate tubes (LBF11, LBF12), each positioned on an electrode (E1, E2) and attached to it with an excess overhang over the end of the electrode (E1, E2).
 2. Optical fiber splicing device according to claim 1 wherein the light arc corona discharge guide (LBF11/12, LBF2, LBF3) comprises a non-electricity conducting, low thermal conducting material comprising ceramic or quartz glass.
 3. Optical fiber splicing device according to claim 1 wherein the wall thickness of the tubes (LBF11, LBF12, LBF2, LBF3) are between 1 to 2.5 mm.
 4. Optical fiber splicing device according to claim 1 wherein the inner diameter of the tubes (LBF11, LBF12, LBF2, LBF3) are between 1 to 2.5 mm and correspond to the outer diameter of the electrodes (E1, E2).
 5. Optical fiber splicing device according to claim 1 wherein the electrodes (E1, E2) comprise tungsten.
 6. Optical fiber splicing device according to claim 1 wherein the electrodes (E1, E2) comprise tips formed in a conical manner at the free ends with a cone angle (KW) of 30° and the distance (AE) of the two tips of the electrodes (E1, E2) positioned opposite each other is between 0.5 to 10 mm.
 7. Optical fiber splicing device according to claim 1 wherein the distance (AR) of the tubes (LBF11, LBF12) and an opening (A2, A3) is between 1 to 2 mm.
 8. Optical fiber splicing device according to claim 1 wherein the opening (A2, A3) or the distance between the two tubes (LBF11, LBF12) is provided with a removable cover (AB1, AB3).
 9. Optical fiber splicing device according to claim 8, wherein the cover (AB1, AB3) comprises lighting channels (BK) and cutouts (AF) for insertion of the ends of the optical fibers (F1, F2) and cutouts (ALB) for the electric corona discharge (GEG).
 10. Optical fiber splicing device for substance-determined connection of optical fibers with a device for the approaching of the ends of two fibers, a positioning device for equal axis alignment of the ends of the optical fibers as well as electrodes for producing an electrical corona discharge for the splicing of the ends of the optical fibers, where a corona discharge guide (LBF11/12, LBF2, LBF3) surrounding the electrodes (E1, E2) is arranged in the area of the corona discharge (GE, GEG), the corona discharge guide showing a tube, which is divided longitudinally in such a way that two complimentary longitudinal parts result, where the lower longitudinal part of the tube is fastened to the optical fiber splicing device and the upper longitudinal part of the tube can be positioned onto the lower longitudinal part of the tube in connection with a hinge arrangement of the optical fiber splicing device.
 11. Optical fiber splicing device according to claim 10 wherein the monitoring channels (BK) are arranged in the corona discharge guide (LBF2, LBF3) in the area of the fiber connection point for optical monitoring of the splicing process.
 12. Optical fiber splicing device according to claim 10 wherein the corona discharge guide (LBF3) is formed as a hollow profile with a hollow space (RH) of a rectangular cross-section.
 13. Optical fiber splicing device according to claim 10 wherein the electrodes (E1, E2) are embedded or infused into the material of the corona discharge guides (LBF2, LBF3). 